Flexible, card-type, portable data carrier devices of the type that include an integrated circuit (IC) are known in the art as "smart cards." More generally, herein, "smart card" refers to any portable card-like device which includes one or more electronic components, i.e., active components such as integrated circuits, transistors, and diodes, and passive components such as resistors, capacitors and inductors. As is practiced in the prior art, an integrated circuit (IC) package is mounted on a substrate thereby constituting a module that is, in turn, attached to the main body of the smart card. Smart cards are currently used for a wide variety of applications including prepaid "debit" cards (e.g., phone cards, transit passes, electronic purse), subscriber cards (e.g., bank ATM cards, credit cards, point-of-sale cards), loyalty scheme cards (e.g., frequent flier cards), security access and identification cards, health insurance and service cards (with optional protected memory), GSM (global system management for European cellular phones) cards and encryption/decryption cards.
Some smart cards include electrical contacts which are used to make an electrical connection between electrical circuitry on or within the smart card and an external interface of a reader/writer device. Such smart cards are referred to as "contact-type" smart cards. Other smart cards referred to as "contact-free" or "contact-less" smart cards do not include electrical contacts. Such contact-free smart cards transfer information to and from the smart card through other means such as, for example, an inductive coil formed in or on the smart card for electromagnetically coupling the smart card with an appropriate external interface. Other types of contact-free cards use electrostatic or capacitive couplings for the transfer of data and instructions to and from the card.
The smart card industry is a market that is dominated by silicon and software, but is defined by packaging options. Most smart card companies come from software or card printing environments and are attempting to implement solutions in a card format.
In accordance with the known technique, there are typically two parallel flows in the smart card production process, namely the (1) card manufacturing flow and (2) the module manufacturing flow. In the card manufacturing flow, the card body is prepared as a subassembly. Popular techniques for producing the card bodies include: (1) a laminated process in which printed layers of polyvinyl chloride (PVC) are laminated together; and (2) an injection molding process using a composition of plastics which may include acrylonitrile butadiene styrene (ABS) resin, polyester, polyvinyl chloride (PVC), polycarbonate, or polyethelynetelephthalate (PET) or a combination thereof The module manufacturing flow includes the steps of attaching the IC package or chip to a substrate, wire bonding, encapsulation, etc. The two parallel process flows are carried out separately and then converge at the point where the module subassembly is embedded within or attached to the card body subassembly. The packaging environments for commercially available smarts cards are very rudimentary and at most consist of un-reinforced plastic.
Smart cards must be flexible and at the same time sufficiently mechanically robust in order to withstand the stresses (bending and torsion) that are encountered during normal use. According to the International Standards Organization (ISO), the maximum allowable thickness of a smart card is 0.033 inches (0.84 mm). Consider, for example, the case of the standard smart card construct having a maximum allowable thickness of 0.033 inches (0.84 mm) and an embedded micro-module having a thickness on the order of 0.024 inch (0.61 mm). The remaining 0.009 inch (0.23 mm) of card material beneath the module presents a weak point on the card. The thickness of card material beneath the module and the position of the module in the card are major design parameters when the resistance of the card to mechanical bending or twisting forces is considered. A widely practiced technique to minimizing the strains transmitted to the module is to position the module in one of the corners of the card. However, this approach limits the size, number and location of modules and/or other electronic components that can be placed in the card.
The reinforcement of a micromodule by means of a metallic "Dam Wall" is practiced. It is also known from the prior art to incorporate reinforcement structure to the card body during the card manufacturing flow to provide added mechanical robustness to the smart card. For example, there is disclosed in U.S. Pat. No. 5,673,179 several techniques for incorporating reinforcement structure within one or more layers of the flexible smart card body in order to protect an integrated circuit module carried by the smart card. The reinforcement structure, having a modulus of elasticity higher than that of the plastic material card body, relieves stress on the integrated circuit module during bending and torsion of the card. The reinforcement structure comprises a separate layer of rigid material that is inserted in the card body during manufacture of the card and is preferably positioned so that it lies beneath or adjacent to the module when introduced to the card. In the conventional card manufacture, the presence of the added reinforcement layer beneath the module further limits the size (i.e., thickness) of module that can be safely and reliably carried by the card.
Whereby the prior art smart card constructions are adequate for small semiconductor devices or single chip modules, the nature of the card materials provide inadequate mechanical and environmental protection for advanced (i.e., larger) chips and multi-chip modules. Accordingly, a mechanically robust smart card capable of carrying larger and more sophisticated semiconductor chips would constitute a significant advance in the art.
However, merely increasing the size of the integrated circuits in the smart cards introduces yet another problem as the bigger chips generate more heat than can be tolerated by conventional plastic card bodies. Plastics become mechanically unstable at temperatures in excess of 50.degree. C. Another important consideration is heat dissipation. The performance and capacity of the IC depends in large part on the ability of the packaging environment to radiate heat away from the IC. Again this must be accomplished in a manner that does not materially effect the mechanical stability of the plastic card body.
Accordingly, a module packaging arrangement for a conventional plastic smart card that enables the card to support larger, more sophisticated chips operating above 50.degree. C. and at the same time provide for efficient heat dissipation would be extremely desirable.